Canberra trip – APRS / GPS logger

I had occasion to make a trip to Canberra for a few days this week.

OpenLog07

It presented as a good opportunity to explore APRS by VHF radio and the stand alone GPS logger above attached to the case of the TinyTrak 3+. The transmitter is 65W output to a quarter wave in the middle of the wagon roof.

Over the three days, the extract from findu was 6240 APRS records (the vehicle was in a covered car park by night), and 389693 NMEA records (~20MB) logged to the logger, from which 6150 track records were extracted using GPSBABEL for track simplification. Both track sources were converted to kml files.

googleearth 14/01/16 , 07:57:54 Google Earth

Above is a screen shot comparing the track around Majura park for GPS logger in red and APRS in cyan. There are several instances of false double backs on the APRS track (a problem inherent to APRS and quite common), and very coarse track despite being less than 8km from the prominent digi on Black Mountain, and very good view of the digi on Mt Ginini.
Continue reading Canberra trip – APRS / GPS logger

Panasonic NCR18650B Lithium Ion cells on eBay

Further to 18650 Lithium Ion cells on eBay I purchased a pair of Panasonic NCR18650B cells, nominal 3400mAh, from an Australian supplier for about A$22 posted.

NCR18650B

Above is a pic of a cell.

NCR18650B02

Above is a zoomed in view of the same pic with increased contrast. The feint QC code printed on the underlying steel container is visible. It is usually visible through the jacket on genuine Panasonic cells.

It is always hard to know whether the product is genuine, the Chinese are better at copying the looks than the internals.

The cell was charged, then discharged at 1C on a battery analyser.

Screenshot - 15_01_16 , 03_12_18

Above is the first three discharge cycles, the cell achieved just under 3000mAh to 2.8V, about 93% of datasheet rated capacity of 3200mAH, 85% of the advertised nominal 3400mAh capacity.

Screenshot - 14_01_16 , 18_39_55

The actual discharge curve is fairly similar to the 1C curve from the datasheet.

These cells look more promising than the GTL red 5300mAh cells previously evaluated.

ANS T1.523-2001, Telecom Glossary 2000 and Return Loss

A correspondent has suggested to me that my practice of giving Return Loss as a positive dB value is wrong, citing US FS-1037C.

US FS-1037C has been superseded by ANS T1.523-2001, Telecom Glossary 2000, and the wording in the latter is identical to the former, so let’s discuss the more current document. Continue reading ANS T1.523-2001, Telecom Glossary 2000 and Return Loss

Update for FSM software (v1.11.0)

FSM has been updated to v1.11.0.

The update adds an export to Gnuplot file of the wave file to allow visual examination of the recording on which the measurements is based.

This replicates the utility of the existing Dplot export, but with the freely available Gnuplot package.

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Above is an example of the receiver noise recording, and whilst it might not seem very interesting, it is interesting that it is of the character of white noise.

Of more interest are cases where there is a distant cyclic pattern at twice the AC power frequency which hints insulator failures on each half cycle. Some other types of periodic modulation are helpful in identifying possible sources of emissions.

References

  • Duffy, O. 2005. Field Strength Meter software (NFM). https://owenduffy.net/software/fsm/index.htm (accessed 11/01/2016).

On negative VSWR

(Terman 1955) gives a meaning for the term SWR (or VSWR).

The character of the voltage (or current) distribution on a transmission line can be conveniently described in terms of the ratio of the maximum amplitude to minimum amplitude possessed by the distribution. This quantity is termed the standing wave ratio (often abbreviated SWR)…

Standing-wave ratio=S=Emax/Emin

Note that the use of capital E implies the magnitude of voltage, so Emax/Emin must always be a positive number.

Lossless line example

Let’s look at an example of a 5Ω load on a line with Zo=50+j0Ω at 0.1MHz.

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The standing wave is observable, the expression VSWR=Emax/Emin seems straight forward enough. The voltage along the line could be sampled and VSWR determined, seems all very practical. Continue reading On negative VSWR

18650 Lithium Ion cells on eBay

I have been intrigued by the huge number of sellers of very low cost 18650 Li-ion cells on eBay.

Could they be any good?

As a reality check, Panasonic cells around 3000mAh sell through traditional channels here in Australia for around A$20 per cell, there are Australian eBay sellers selling cells advertised as Panasonic for around A$22 per pair posted.

GTL01Above, the GTL red LS18650 5300mAh Li-ion cell purchased in a lot of five for $1.30 each (inc post from China).  The rated capacity is more than 50% higher than the maximum from brand name products. Continue reading 18650 Lithium Ion cells on eBay

Quiet solar radio flux interpolations calculator

Further to the posting Quiet solar radio flux interpolations calculator

With a change in hosting and the changes to adapt to supported and unsupported features, one of the positives is that the ‘short term’ fetching of data on which Quiet solar radio flux interpolations calculator is based is now happening two hourly at 5 minutes past the even hours. Continue reading Quiet solar radio flux interpolations calculator

NEC model of the quarter size G5RV

Fractional G5RV antennas seem very popular in the US market, and they appeal to hams wanting multi band performance in small space.

One of the offerings is the quarter size G5RV, commonly marketed as the G5RV Mini.

The original concept set out by G5RV was a combination of a centre fed dipole and open wire transformation section to successfully deliver a lowish VSWR(50) on several of the pre-WARC bands. This enabled arbitrary length low Z feed extension to the transmitter, and allowed direct attachment to transmitters of the common design of the day (1950s). Continue reading NEC model of the quarter size G5RV

WSPR version confusion

Investigation whilst developing Evolution of WSPR revealed some potential issues relating to certain WSPR versions.

The WSPR 2.0 manual states:

Please note that messages with compound callsigns or 6-digit locators will not be properly decoded by WSPR versions earlier than 2.0. Further details on message formats can be found in Appendix B, and in the WSPR source code.

So, lets mine some data. Continue reading WSPR version confusion